1. Field of the Invention
This invention relates to the field of communication systems. In particular, the present invention relates to the providing synchronized clock signals for a plurality of remote devices within a synchronized CDMA communication system.
2. Prior Art
When transmitting information signals between a base station and a plurality of remote network terminals (RNTs) within a synchronous CDMA communication system, the clock signals of the RNTs and the base station of the communication system must be synchronized with each other in order to accurately communicate the information signals. For example, within a synchronous CDMA communication system, whereby each RNT has a 4.096 MHz PCM clock, it is advantageous to synchronize the PCM clock with the very stable pseudorandom number (PN) clock of the base station.
The RNT typically recovers the PN clock signal from a PN signal received with the global pilot signal transmitted by the base station. The RNT may use the recovered PN clock signal as a reference signal to provide synchronization for the PCM clock within the RNT. For example, the recovered PN clock signal may be divided by the processing gain of the system to provide a sixty-four (64) kHz reference signal. The 64 kHz reference signal may then be multiplied by 64 in order to provide the synchronized 4.096 MHz PCM clock required by the RNT for clocking its circuitry.
However, this approach requires a significant amount of extra circuitry within the RNT in order to recover the clock signal for use by the RNT and perform the required operations upon the recovered clock signal. Furthermore, this approach requires frequency multiplication operations to provide the desired frequencies. Since these frequency multiplication operations cause any noise present in the multiplied signal to be multiplied along with the frequency of the signal, the clock signal provided by this approach could include a substantial amount of jitter. Furthermore, if constant phase adjustments of the reference clock are required to compensate for frequency wandering of the reference clock, further jitter may be introduced into the reference clock signal.
Accordingly, it would be desirable to provide a clock signal within an RNT of a communication system that is synchronized to the PN clock of the base station whereby the synchronized clock signal provided in this manner has low jitter and does not require substantial additional circuitry.
In a CDMA communication system having a received PN clock signal, a method is disclosed for providing a synchronized system clock signal having reduced jitter wherein the synchronized system clock signal is synchronized with the received PN clock signal. The method includes providing a stable high frequency reference signal and dividing the high frequency reference signal to provide a system clock signal having a plurality of system clock phases. The method also includes adjustably selecting a system clock phase of the plurality of system clock phases in accordance with the received PN signal to provide the synchronized system clock signal. The received PN clock signal is recovered by providing PN phase adjustments of the received PN clock signal. A tracking control signal is provided in accordance with the PN phase adjustments and the system clock phase is adjustably selected in accordance with the tracking control signal. The high frequency reference signal can be multiplied prior to the dividing.